UNITED NATIONS — U.N. inspectors found “clear and convincing evidence” that large quantities of the nerve gas sarin were used last month in Syria, the first confirmation by an internationally recognized team of experts that a chemical weapons attack took place.

The inspection report, presented to the U.N. Security Council on Monday, does not assess blame for the attack. But underlying evidence included in the report, including the trajectory of ­poison-filled rockets, was cited by the United States and its Western allies as proof of the Syrian government’s responsibility.

The inspectors’ conclusion “confirms the position of those of us who have said the regime is guilty,” French Foreign Minister Laurent Fabius said.

U.N. Secretary General Ban Ki-moon called the findings “beyond doubt and beyond the pale,” and a clear evidence of a war crime.

“The results are overwhelming and indisputable,” Ban said. “Eighty-five percent of the blood samples tested positive for sarin. A majority of the environmental samples confirmed the use of sarin. A majority of the rockets or rocket fragments recovered were found to be carrying sarin.”

International confirmation that the attack took place seemed anticlimactic after the events of last week, when Syria acknowledged for the first time that it possesses chemical weapons and agreed to surrender them, and the United States and Russia negotiated a plan to carry out the handover.

Syria and Russia still say the Aug. 21 attack in the suburbs of Damascus was perpetrated by rebels seeking to overthrow Syrian President Bashar al-Assad.

Under the U.S.-Russia agreement, Syria must provide an inventory of its chemical stockpiles by the end of this week to the Organization for the Prohibition of Chemical Weapons, based in The Hague. The OPCW, the body that carries out the international Chemical Weapons Convention, said Monday that it would begin drawing up a plan to “eliminate” the arsenal within “a matter of days.”

Inspection of Syria’s estimated 1,000 metric tons of poison material would begin in November, with destruction to take place next year.

Also Monday, President Obama signed an order waiving arms-control restrictions on the export of protective equipment and the provision of training to Syria. The action allows the shipment of U.S. gear to the OPCW for use in Syria, and permits equipment and training to be provided to nongovernmental organizations working with Syrian civilians and to approved rebel groups to shield themselves against any further chemical attacks.

A threat of force?

The U.S.-Russian road map also calls for a Security Council resolution that would punish Syria if it did not comply with the agreement. As council members debated its terms, Russian Foreign Minister Sergei Lavrov criticized what he called “distorted” reports that it might include a threat of military force.

Vitaly Churkin, Russia’s U.N. ambassador, said suggestions that Russia has given “blanket” support for such a resolution mean the agreement is being “misinterpreted and misused by those who from time to time keep looking for a pretext to use military power.”

The agreement specifically refers to a resolution under Chapter 7 of the U.N. Charter, which includes a provision on the use of force. But diplomats from Security Council member nations, speaking on the condition of anonymity about the closed-door discussions, said the resolution would more likely be governed by a different provision authorizing measures short of military action.

The diplomats referred to a Chapter 7 paragraph that suggests steps that include “complete or partial interruption of economic relations and of rail, sea, air, postal, telegraphic, radio, and other means of communication, and the severance of diplomatic relations.”

If such measures prove “inadequate,” the chapter says, the Security Council “may” take military action “necessary to maintain or restore international peace and security.”

The distinction is an important one, because a council veto by Russia or China of any proposed resolution would probably upend the chemical weapons agreement.

As part of the accord, Lavrov and Secretary of State John F. Kerry agreed to devote new energy to convening a peace conference between the opposing sides in Syria’s civil war. Progress toward the conference, first agreed to earlier this year, has been elusive.

Assad and his Russian backers have rejected opposition demands that he be excluded from the conference and ultimately step down, and the opposition has never formally agreed to attend.

At a Moscow news conference, Lavrov indicated that the United States should be able to deliver the rebel delegation.

“First it was necessary to convince the opposition to participate in that conference, and now it is probably time to use another verb and force the opposition to participate,” Lavrov said, according to Russia’s Interfax news agency.

He said that he, Kerry and U.N. envoy Lakhdar Brahimi had agreed in talks last week that the conference should take place in Geneva “sometime in October.” Lavrov said, “We are ready to begin making arrangements even tomorrow.”

‘The pressure is on’

Kerry met in Paris on Monday with Fabius and his counterparts from Britain and Turkey to brief them on the terms of the agreement. He also met with Saudi Arabia’s foreign minister, Saud al-Faisal.

British Foreign Minister William Hague did not specify his government’s bottom line for a new Security Council resolution but said that “the pressure is on [Syria] to comply with this agreement in full. The world must be prepared to hold them to account if they don’t.”

Kerry went further. The chemical weapons deal “has to be enforced,” he said. “If the Assad regime believes that this is not enforceable and that we are not serious, they will play games.”

In Washington, Sen. John McCain (R-Ariz.), who has been among the loudest congressional voices urging a strike against Syria, said that without a military option, the weapons agreement is “not enforceable” and has “no credibility.”

“What they are promising is a laudable goal, but there is no real way to achieve it,” McCain said in an interview with CNN.

Kerry and McCain spoke before the release of the U.N. report, which was first presented to Ban on Monday morning by Ake Sellstrom, the head of the inspection team that visited the site of the Aug. 21 attack within days after it occurred.

Sellstrom’s team compiled evidence from a broad range of sources, including statements from more than 50 victims, first responders and medical specialists. The team also examined pieces of surface-to-surface rockets “capable of delivering significant chemical payloads,” the report said. Sarin was identified in the majority of the fragments, as well as in environmental and biomedical samples, including blood, urine and hair from the victims.

The 38-page document did not estimate the number of victims in the attack, which U.S. officials have said killed more than 1,400 people, including more than 400 children.

“Survivors reported an attack with shelling, followed by the onset of a common range of symptoms, including shortness of breath, disorientation, rhino­rrhea (runny nose), eye irritation, blurred vision, nausea, vomiting, general weakness, and eventual loss of consciousness,” the report said. “Those who went to assist . . . described seeing a large number of individuals lying on the ground, many of whom were deceased or unconscious.”

DeYoung reported from Washington. Anne Gearan in Paris contributed to this report.

Karen DeYoung is associate editor and senior national security correspondent for the Washington Post.

Comments our editors find particularly useful or relevant are displayed in Top Comments, as are comments by users with these badges: . Replies to those posts appear here, as well as posts by staff writers.

To pause and restart automatic updates, click "Live" or "Paused". If paused, you'll be notified of the number of additional comments that have come in.

Comments our editors find particularly useful or relevant are displayed in Top Comments, as are comments by users with these badges: . Replies to those posts appear here, as well as posts by staff writers.